The invention relates to a dashpot for fuel tanks of the type having a cover which tapers in the direction of an opening and a jet pump in a base region for the fuel flowing back from a fuel injection installation for an internal combustion engine. A suction filter is disposed in the interior of the dash pot.
A dashpot of this kind is known from DE-PS 2,401,728. In an alternative solution to the pot construction shown, its cover forms a funnel which is explained. The purpose of this funnel is to catch, in the dashpot, fuel sloshing over the latter in the fuel tank and thereby ensure increased introduction of fuel into the pot interior.
For supplying internal combustion engines with fuel, in particular those having fuel injection, it is customary for more fuel to be supplied than is necessary for combustion. During this process, unconsumed fuel is heated, in particular on its way along hot zones, giving rise to gas bubbles in the fuel return line. When this heated fuel flows out of the pump channel of the jet pump opening into the dashpot, the gas bubbles expand and rise upwards. When the dashpot is filled to the maximum, the gas bubbles collect in the annular space, closed towards the top, which is formed by the conical shell surface of the cover tapering into the pot interior and the upper part of the pot wall. The gas bubbles are displaced from the annular space, necessarily moving inwards and obliquely downwards in the dashpot along the conical shell surface of the cover before reaching the opening in the central part of the cover and being able to escape. On their way to the opening in the cover, the gas bubbles at the same time come close to the suction filter, with the result that gas is also drawn off with the fuel to be drawn off.
However, similar conditions are also present if the cover forms a flat lid. In this case, the gas bubbles then rest against the lower surface of the lid and are displaced radially inwards to the opening in the lid, likewise coming close to the suction filter, with the result that in this case too gas is also drawn off together with the fuel.
An object of the invention is to improve the discharge of gas bubbles and to keep gas bubbles away from the suction filter in a dashpot of the above-noted type.
This object is achieved according to the invention by providing a dome shaped cover which is arranged at a spacing above the suction filter.
Because of the dome-like shape of the cover, ascending gas bubbles can collect against the inner surface of the cover far above the suction filter and, during their further upward movement towards the opening of the cover, can move upwards away from the suction filter.
In preferred embodiments the pump channel opens into a guide channel which discharges into the pot interior and is of increasing height in the direction of the inflowing fuel. This arrangement ensures that the fuel flowing into the dashpot and permeated with gas bubbles is prevented over a relatively long section from mixing with fuel already in the pot interior containing the suction filter and that ensures that the fuel loses its gas content during this procedure. During this procedure, the mass of gas bubbles is already able to coalesce at the upper channel wall along the channel region and move upwards along said channel wall. In this arrangement, the height of the guide channel, which increases in the direction of flow of the fuel, causes the gas bubbles to float obliquely upwards, with the result that, when the fuel enters the pot interior, the gas bubbles are already near the highest region of the space and are thus correspondingly distant from the suction filter.
In certain preferred arrangements, it is advantageously provided that the upper channel wall of the guide channel extends in a spiral as far as the pot cover.
In certain preferred embodiments of the invention the upper wall part of the guide channel adjoins the discharge point of the pump channel in the region of the smallest channel height and delimits the discharge point at the top. This arrangement ensures that fuel flowing out of the pump channel of the jet pump cannot become turbulent downstream of the channel exit or cannot become turbulent to such an extent that fuel can thereby foam and result in increased gas bubble formation.
In especially preferred embodiments the pot and channel walls, the cover, part of the pump channel and injection nozzle are formed as an integral molded part, which makes it possible to produce the dashpot from only two individual parts (upper pot part and pot base), which can be produced by the injection method, it being possible to align and shape the injector nozzle and the pump channel of the jet pump in an optimum manner with respect to one another.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.